True, but can they pick up ruby quickly, and rails (rails is non trivial these days), and rspec, and rake, etc. I'm guessing it would take at least 6 months to become merely comfortable with all of these. This is far different than having a proficient coder walk in the door.
You'll have much better luck getting a proficient rails coder than a proficient django coder. On the flip side I'm starting to get a lot of rails candidates that aren't really interested in rails, but used it at their previous job. For while if someone had rails on their resume it meant they took the time to learn it on their own (which is a good sign). Those days are gone.